Shell-side condensation of HFC-134a and HCFC-123 on enhanced-tube bundles
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For the past five decades, CFCs (chlorofluorocarbons) have been some of the primary working fluids used in vapor-compression refrigeration devices. In recent years, CFCs (such as CFC-12 and CFC-11) have been found to destroy the Earth's protective ozone layer, and current mandates require that all new refrigeration equipment produced after 1996 must use an ozone-safe refrigerant. Currently, HFC-134a is targeted as the replacement for CFC-12, and HCFC-123 is targeted as a near-term replacement for CFC-11. The purpose of the present study was to obtain experimental performance data for the shell-side condensation of HFC-134a and HCFC-123 on enhanced tube surfaces. The data obtained in this study will be used to aid engineers who design shell-and-tube condensers for vapor compression refrigeration systems utilizing HFC-134a and HCFC-123;Shell-side condensation heat transfer data were obtained for refrigerants HFC-134a and HCFC-123. In addition, CFC-12 and CFC-11 data were obtained for comparison purposes. The tube bundles used in this study were constructed from 19.1 mm (0.75 in) o.d. 1024-fpm (26-fpi), 1575-fpm (40-fpi), Turbo C-II, and GEWA SC tubes. The tube bundles tested are 5 columns wide by 5 rows deep and have a staggered tube arrangement with a horizontal pitch of 22.2 mm (0.875 in) and a vertical pitch of 19.1 mm (0.75 in). The data were obtained at a refrigerant saturation temperature of 35°C (95°F) over a bundle heat flux range of 18 000-40 000 W/m[superscript]2 (5700-12 700 Btu/(hr·ft[superscript]2)). Average condensing heat transfer coefficients for the bundle as well as average condensing heat transfer coefficients for the middle tube of each row were calculated;For a given tube geometry, the performance of HFC-134a was generally 20% better than the performance of CFC-12, while the performance of HCFC-123 was generally 20% better than the performance of CFC-11 at low heat fluxes, and 10% better at high heat fluxes. For HFC-134a, the performance of the Turbo-CII was two to three times better than that of the other tube geometries, and 1.25 to 2 times better than the other geometries for HCFC-123.